Apparatus for the explosive pulverization of coal



Feb. 9, 1954 1 F, SKELLY 2,668,669

APPARATUS FOR THE'. EXPLOSIVE PULVERIZATION OF COAL Filed sept. 18, 1947'ATTORNEYS atented Feb. 9, 195:4

APPARATUS FOR THE EXPLOSIV PULVERIZATION F COAL Joseph F. Skelly, NewYork, N. Y., assignor to The M. W. Kellogg Company, Jersey City, N. J.,a

corporation of Delaware Application September 18, 1947, Serial No.774,867

2 Claims.

This invention relates to the explosion pulverization or coal and moreparticularly to an improved method and apparatus for verticallyclassifying the explosion pulverization products in a mass of coalparticles which is maintained in a fluidized condition by introducingthe explosion products upwardly through said mass.

Recent developments of new products and processes employing nnelydivided coal have been hampered in attaining commercial standing becauseof the high cost of reducing the coal to pulverized condition by methodsheretofore known. For instance, a fuel comprised of oil containingcolloidally suspended coal particles has been limited in applicationbecause no economic method was available for producing suficientlypulverized particles. It is a primary object of this invention toprovide a commercially practicable method for powdering coal byexplosion pulverization and an apparatus adapted for the employment ofsaid method.

Although explosion pulverization has been previously prop-osed as ameans for coniminuting permeable substances by permeating the particleswith a uid under pressure and then suddenly reducing said pressure, suchprocesses have never met with commercial success for the powdering ofcoal. One of the principal reasons for this failure has been that thepulverization process has been found to pulverize only a minorproportion of the particles subjected to the pressure reduction step.The balance of the particles must be recycled through the process fornew treatment. It is an object of this invention to provide an eilicientand economical means for classifying the products of explosionpulverization into those particles which have been suflicientlypulverized and those which are adapted to be subjected to explosionpulverization. If desired, a third classification of the particles toolarge for explosion pulverization may be withdrawn for recycling to apreliminary mechanical grinder.

A further disadvantage of previously known explosion pulver-izationmethods as applied to pulverizing coal, has been encountered in thediiilculty and cost of increasing the pressure on the granulated coalpreparatory to explosion pulverization. An object of the presentinvention is to provide a method and apparatus by means of which knownfluid pumping means may be employed to increase the pressure on saidgranulated coal material.

These objects and other objects, which will become apparent from thedescription of a typical application of the invention, are achieved byemploying a large iuidized mass of particles which are maintained in aturbulent circulatory condi- A tion so that the particles thereinclassify themselves vertically with the heaviest particles near thebottom of said mass, the lightest particles in the upper portion of saidmass, and particles of intermediate size according to elevation. In thepreferred form of my invention this turbulent luidized condition of themass of particles is maintained by introducing upwardly therethrough amixture of particles and gas which is the product of explosionpulverization; that is, after the mixture of particles and the gaseousexplosion pulverization medium have experienced a sudden reduction inpressure from a substantially elevated pressure to a pressure onlyslightly greater than that prevailing in the mass of fluidizedparticles, this mixture is introduced, usually through a plurality ofopenings through the bottom of a vessel containing the fluidized mass.

Although the invention may be employed for the explosion pulverizationof materials other than coal, or for the explosion pulverization of coaland other materials with a great variety oi' vapors (mercury or Zincvapors, for instance) or gases (such as air, nitrogen, or hydrocarbons),the process has been developed primarily for the explosion pulverizationof coal by means of steam vapor, for which the process is uniquelyadapted. It has been found that most coals have a crystalline structureand a degree of permeability such that it is desirable to apply theexplosion pulverization method to coal granules of a predeterminedmaximum size, which may be found experimentally in the case of eachparticular type oi coal. For this reason, the system is uniquelyvaluable for explosively pulverizing coal on a large commercial scale.Furthermore, since steam is relatively cheap and non-reactive with coal,it is a preferred explosion medium for the presently disclosed process.

A typical embodiment of an apparatus suitable for practicing my methodis illustrated in the accompanying drawing. Coal enters the apparatus atIii and is ground in grinder II to a coarse feed powder (a number 4 meshhas been found quite suitable) and delivered to a large feed hopper I2from the bottom of which the coarse coal is fed into a large vessel 53containing a iluidized bed I4, the nature of which will be described indetail hereinafter. The feed may be introduced by a solids pump, astandpipe, or any other eiective device; in the present embodiment theelevation of the hopper I2 gives some standpipe effect; a spiralscrew-type of feeding means is indicated diagrammatically at i5. Theexact point in the vessel at which the feed is introduced is not veryimportant, but in most cases best results are obtained by introducingthe coarse powder into vessel I3 near the top of iluidized bed Ill.

The iluidized mass I4 is comprised of particles of coal which aremaintained in a pseudo-liquid 3 or "iluidized bed by continuouslyintroducing upwardly through said bed a gasiform iluidizing medium. 'Theterm Y'gasiform rather than gaseous is used here f'si-nce theYiiu'idizing medium may -not be a true gas -but may be, for instance, amixture of gas and solid particles which is much less denseV than thebed of particles Within vesseli and is capable of flowing thereinto andtherethrough in,Y

the manner of a fluid under pressure. The fluidized condition thusproduced in bed i4 'is 'characyterized by the relatively highconcentration of particles of solid material per unit volume of occupiedspace, and maintained by the low velocity` oW of fluidizing mediumupwardly through the bed. The maintenance of a denite minimum gaseousvelocity is regarded as desirable to maintain "the bed in a turbulent'fluidized state in which 'the-particles tend to A:move among onevanother in a 'circulatory manner. Preferably, the upward `velocity Aofthe gas through the fluidized bed i4 is As'uiliciently high to -maintainsufficient turbulence in the bed so that any given elevation within Ves--sel I;3, ythe smaller and lighter particles will tend 'to'drift in'an-upward direction and the larger and heavier vparticles in a downwarddirection with a result that the entire fluidized bed I4 tends toclassify itself according to particle size ranging from the heaviest4particles at the lowest point to the Ylightest particles vnear theupper surface i6 of iluidized bed I4. The optimum velocity of a`fluidizing medium, both with respect to its minimum and maximum value,will ibe dependent lupon the density, size, and shape of the solid:particles being iluidized and upon the properties :of lthe uidizingmedium. Thus, for any particular'size or sizes of particles and qualityof fluid- Yizing medium this velocity is adjusted within a range so-as'to maintain the desired turbulent but dense condition of fluid-bed I4.

The finest particles `within the fluidizing bed Eli will Abe carried bythe fluidizing medium, which the present preferred embodiment iscomposed principally of steam, upwardly from the surface i601-fluidizing bed I 4 through line il. In the event that this overheadmaterial is not as inely ground as desired, it may be passed to aseparator I8 which will vremove coarse particles vand @return them toVrvessel I3 Ithrough line i3. This l'separator may be of conventionaldesign, such as cyclone separator of proper particle size selecltivity.It is best to return the oversized particles -frorn'this separator -to apoint well below the tcp of the dense iluidized bed I@ to prevent theirimmediate reentrainment in the mixture of finely powdered coal by steamescaping through line i'i. 'Ihe nelypowdered overhead product withdrawnfrom Vessel I4 through line I'I and, if desired, freed of oversizedparticles from separator i8 is jthen passed by conduit'E to any suitablemeans 2i 'for separating the solid particles from the steam. Thenely'pulverized coal product may be withdrawn from means 2l at 22 andthe particle-free steam -may be withdrawn through line 23 to be 'reusedin the process.

By far, the greater portion of the coal introduced into vessel I3vthrough feeding means i5 will not be sufficiently fine to pass overheadthrough line I? and will settle downwardly l'through the vessel I3 to beclassified at various elevations according to size as heretoforeldescribed. If desired, the heaviest particles may be withdrawn from thelower `portion of the vessel I3 and recycled to the grinder I I throughconveyngrmeans 24. y

Those particles which are of a size adapted to the particular method ofexplosion pulverization being employed will tend to classify themselvesat some particular elevation Ywii-,hirr iluidized mass I4. Thiselevation will focclur -dependent on the type of coal and the percentageof lines produced `by grinder I I. A plurality of withdrawal pipes 25,26 and 27v are, therefore, provided for Withdra'wing iluidized coal fromvarious elevations vwithin fluidized mass I4. The fluidized material sowithdrawn is delivered to one or more lock hoppers 28 and 29; a pump 30may be employed for this purpose, lhowever, in most instances it will befound preferable to eiect the movement of -luidized material YfromIluidized bed I4 to lock hoppers 28, and 29 merely by a difference inpressure head.

In the preferred embodiment zone, fluidized material from vessel I3 --isintroduced into lock hopper 28 through valve 3l at a relatively lowpressure wln'le at the same time entrance of material into lock hopper29 is prevented bythe closure of a valve 32. After lock hopper 28 islled, valve 3| is closed and 32 is opened and fluidized material isVpermitted to now from vessel I 3 into lock hopper 29. Lock hopper 28 isprovided with outlet valve 33 which is closed while valve 3l is openedand hopper 28 is being lled, after which it is opened to permitiluidized products to flow -downwardly from the lower portion of hopper28 into pipe 34 through which itis driven by steam at high pressurethrough an explosion pulverization nozzle 35 or any other'suitable meansfor suddenly reducing the pressure-on the fluidized material. Fromexplosion pulverization means 35 the low pressure steam produced and thecoal particles entrained therein are passed through line 36 to vesselI3, preferably through ports 37 in the bottom thereof, to flow upwardlythrough iiuidized bed I4 and maintain it in a fluidized condition.

After hopper 28 has been emptied, valves 32 and 33 are closed and atthesame time -valve3I-is opened to permit hopper 23v to be refilled and theoutlet valve 42 of hopper 29 is opened to permit its contents to besubjected to high .pressure by the high-pressure steam in line 34 and-topermit flow of the high-pressure uidized material from hopper 29 intoline 34 and thence to explosion pulverization means 35. Lock hoppers `28Vand A29 are thus operated ultimately to maintain asubstantiallycontinuous ilow of dense iluidized material from vessel I3 to one of thelock hoppers and a substantially continuous -ow of low-pres.- sure steamand explosion pulverization products from explosion pulverizationmeans35 upwardly through ports 3l Yinto vessel I3. Steam entering vessel I3through ports 3l is, of course, of sufficiently high pressure toovercome the pressure head existing because of the depth -of iluidizedbed I4. Also, since the low-pressure steamand coal particles produced bythe explosion pulverization means 35 are of much lower density thaniluidized bed I4 and, therefore, serve admirably as a iluidizing medium.v I

The greater portion-of the high-pressure steam required to be introducedinto line 34 for the eX- plosion pulverization step is obtained :byrecompressing in compressor 38 the low-.pressure steam separated fromthe Apulverized product material by separator 2l. A steam generatingsource 3,9is provided for starting and forl providing vmake-up steamduring the operation of the process vif necessary. It is desirable toprovide a-sumpv40 at some point in the systemfor withdrawing from itcondensed steam, which may bev recycled through a pipe 4I to the steamgenerating means 39. In operation, surface level I6 of dense Huidizedmass I4 is maintained by continuously supplying through screw conveyormeans I5 coarse coal ground by grinder II to a preliminary fineness. Theiluidized bed I4 within vessel I3 is maintained at approximately thesame volume and is of approximately the same character at all timesduring the operation of the process but material is constantly beingwithdrawn through lines 25, 26 and 27 or through any suitablecombination of them to be fed alternately either to lock hopper 28 or29; also, a much smaller quantity of material is being withdrawn asiinished or semi-iinished product through overhead line Il. Of course,only a minor fraction of material passing through explosionpulverization means 35 is reduced to the required iines and it thereforeusually happens that the amount of material being withdrawn from vesselI3 for cycling through the explosion pulverization step is several timesthe amount which is being added during the corresponding period of timefrom hopper I2 or is being withdrawn through overhead line Il.

While one preferred form has been illustrated and described, thisinvention is not limited to the conventional details referred to. Forinstance, some iiuidizing means other than the explosion pulverizationmedium may be continuously pumped into the lower portion of vessel I3,withdrawn from the upper portion, above the surface IB of the densephase of fluidized mass I4, and reintroduced into the lower portion.Such a iluidizing medium may be used independently of the steam, thelatter being employed solely as an explosion pulverization medium. Also,the invention is not limited to a method or apparatus in which thematerials are conveyed from one point to another in fluidized form.Lines 25, 26 and 2l may be any suitable means for transporting aclassified material from vessel I3 to the explosion pulverization step.Similarly, the invention is not limited to the withdrawal of overheadproduct in fiuidized form; any suitable conveying means may be employedfor withdrawing nely pulverized material from the uppermost layers ofclassifying vessel I3. Other parts of this system will also be found tobe readily adaptable to other means of transportation to those skilledin the art. The regrinding of the coarsest material withdrawn from thelower portion of vessel I3 by line 24 is merely a suggestion which maybe of advantage only in certain cases.

The invention is not limited to any particular means of explosionpulverization although it is peculiarly adapted to the combination oflock hoppers and explosion pulverization nozzle illustrated. Theinvention could be combined, however, with other means for raising thepressure on the coarse coal particles preliminary to explosionpulverization. For instance, the coarse coal particles may be formedinto a slurry and pumped to a high pressure before being introduced intosteam line 34, as described in the co-pending application Serial No.774,768, now Patent No. 2,560,807, entitled Method and Apparatus forExplosion Pulverization, and filed by Walter E. Lobo.

I claim:

1. An apparatus for pulverizing material which includes: a verticallyelongated vessel; means for introducing granulated solid material intothe upper portion of said vessel; means for introducing a gasformsuspension medium upwardly through said vessel to maintain particlestherein in a turbulent iiuidized state to cause them to classifythemselves vertically according to size; lock hopper means; means forwithdrawing uidized solid particles from said vessel and transferringthem to said lock hopper means; means for withdrawing said solidparticles under pressure from said lock hoppers and introducing theminto a high pressure gasiform medium to form a suspension and means forsuddenly reducing the pressure thereon to produce explosivepulverization; means for reintroducing the gasiform medium andpulverized solid products from said explosion pulverization upwardlythrough said elongated vessel to maintain the contents thereof in thefluidized condition; means for withdrawing a nely pulverized productfrom the upper portion of said vessel; and means for withdrawing andrecompressing gasiform medium from said vessel for reuse in saidpressure reducing means.

2. An apparatus for pulverizing material which includes: aclassification vessel; means for introducing granulated solid materialinto said vessel; means for introducing a gasiform suspension mediumupwardly through said vessel to maintain particles therein in aturbulent fluidized state to cause them to classify themselvesvertically according to size; lock hopper means; means for withdrawingfluidized solid particles from said vessel and transferring them to`said lock hopper means; means for withdrawing said solid particlesunder pressure from said lock hoppers and introducing them into a highpressure gasiform medium to form a suspension; means Vfor suddenlyreducing the pressure thereon to produce explosive pulverization; meansfor reintroducing the gasiform medium and pulverized solid particlesfrom said explosion pulverization upwardly through said elongated vesselto maintain the contents thereof in the iiuidized condition; and meansfor withdrawing a finely pulverized product from the upper portion ofsaid vessel.

JOSEPH F. SKELLY.

References Cited in the ille of this patent UNITED STATES PATENTS NumberName Date 530,635 Blackman Dec. 11, 1894 1,748,920 Newhouse Feb. 25,1930 1,791,100 Lykken Feb. 3, 1931 1,922,313 Mason Aug. 15, 19331,984,380 Odell Dec. 18, 1934 2,154,784 Stump Apr. 18, 1939 2,159,849Graemiger May 23, 1939 2,310,894 Brusset Feb. 9, 1943 2,315,084 CheslerMar. 30, 1943 2,318,306 Hanna May 4, 1943 2,337,162 McCleary Dec. 21,1943 2,372,514 Pootjes Mar. 27, 1945 2,379,077 Harding June 26, 19452,421,212 Medlin May 27, 1947 2,560,807 Lobo July 17, 1951 2,568,400Keargy Sept. 18, 1951 FOREIGN PATENTS Number Country Date 268,188 GreatBritain Mar. 31, 1927 OTHER REFERENCES Chemical Engineering Progress(vol. 43, No. 8, pp. 429), title Fluidizing Processes."

Chem. 8; Met. Eng., Feb. 1941, pp. 122-125, 83 Exp. Dis.

